1. Field of the Invention
The present invention relates generally to an ink jet apparatus. More particularly, the present invention relates to an ink jet apparatus which assures that each recording operation can be performed with excellent gray scale (gray level) level properties.
2. Description of the Related Art
As is well known, much attention has been paid to an ink jet system especially in consideration of the fact that since the ink jet system is operated in accordance with the principle of a non-impact recording process, the ink jet system exhibits excellent quietness during each recording operation, and moreover, it makes it possible to achieve each recording operation at a high speed, and to form colored images each having excellent saturation on recording paper.
Among plural types of ink jet systems available at present, an ink jet system of the type having thermal energy generated by a heater or the like utilized therefor makes it possible to construct the ink jet system with small dimensions, employ a multi-orifice for executing the ink jet system or arrange a plurality of orifices at a high density.
In practice, the ink jet system having thermal energy utilized therefor in that way has many advantages as mentioned above, but in the case that it is required that images each having a high quality are recorded on a recording sheet, it is desirable that images each including a halftone information are recorded on the recording sheet with acceptable gray scale properties.
As a method of expressing a gray scale employable for an ink jet apparatus, there has been known an ink jet method practiced by ejecting plural kinds of inks (each having a different color or a different density) from each of a plurality of ejection outlets in response to an image signal containing information on a gray scale with a plurality of dots overlapping each other while controlling an overlapping area of overlapped dots or an ink jet method practiced by controlling the timing relationship among a plurality of driving signals to be applied to a plurality of heaters disposed at a single ejection outlet in order to change a quantity (volume) of ink to be ejected from the latter.
With the conventional ink jet system constructed in the above-described manner, however, plural kinds of inks, a plurality of ink supplying systems and a plurality of driving circuit systems are required for expressing a gray scale per a single pixel. As a result, there arise problems that each recording apparatus is complicated in structure, and moreover, it is produced at a comparatively expensive cost.